The present invention relates generally to high-performance transistors, and relates more particularly to the fabrication of ultra thin silicon on insulators.
Ultra thin silicon on insulator (UTSOI) refers to SOIs having an extremely thin layer of silicon (e.g., forty to eighty Angstroms) deposited on a silicon dioxide (SiO2) buried oxide (BOX) layer. UTSOI is often used in the fabrication of high-performance transistors.
Due to the extreme thinness of the silicon layer, contact resistance becomes a critical issue. Attempts to reduce contact resistance have included raising the source and drain of the UTSOI, for instance using selective epitaxial silicon or silicon germanide (SiGe) growth. The temperature of the epitaxial growth in such processes is a critical parameter for proper employment of the raised source and drain technique. For instance, if the temperature is too high (e.g., approximately 800 degrees Celsius or above) the thin silicon layer becomes agglomerated and uneven, resulting in greatly increased contact resistance. However, if the temperature is too low (e.g., less than approximately 750 degrees Celsius), selectivity and growth rate prevent good formation of the raised source and drain.
Thus, there is a need in the art for a method and apparatus for fabricating an ultra thin silicon on insulator to reduce contact resistance.